The present invention relates in general to thin film primary batteries.
Electrochemical elements, i.e. batteries, are known in many different physical forms. In most cases, they have a mechanically robust housing and are in the form of round, button or prismatic cells. A positive and a negative electrode, a separator and an electrolyte are arranged in such a cell. The housing of this type of cells is in general composed of steel, a stainless steel alloy or aluminum.
However, for certain applications very thin batteries having a flexible housing are needed. These applications include active radio frequency identification (RFID) tags, PCMCIA cards, smart cards, etc. A battery which shall be used in such applications must be flexible and compact, deliver high energy density and specific energy with a low rate of self discharge, and should be provided with a reliable sealing. The sealing is extremely important, as moisture should be prevented from entering into the battery to avoid drain and self discharge, as well as to prevent drying out resulting from loosing the organic solvents in the electrolyte, even when the battery is distorted or under mechanical stress. Furthermore, the battery should be manufacturable in a cost-efficient and reliable way.
Different thin film batteries are known from prior art, most of them using lithium as the anode material.
U.S. Pat. No. 5,989,751 for example, discloses a primary lithium battery having a flexible and compact design. The cell is provided with an electrolyte-containing composite cathode. A packaging using a spacer and polymeric sheets is provided.
US 2003/0228517 A1 shows a thin cell with a packaging being formed by two plastic sheets sealed to each other. The thin cells described in this document are stacked to form a larger electrochemical element. The plastic sheets are metallized in certain areas to form the electrical contacts with the electrodes of the cell.
US 2005/0239917 also discloses a thin film lithium battery, wherein the anode is printed on a copper current collector using lithium metal powder based ink. The anode and cathode current collectors are sealed around the perimeter of the battery by a polyester sealant frame.
U.S. Pat. No. 6,752,842 B2 discloses a thin film cell which is manufactured by printing different layers on top of each other.
In terms of quality of the sealing and cost-efficiency upon production, the above described batteries are not yet completely satisfying.